1. Field of the Invention
This invention relates to an interlocking device for a hot isostatic pressurizing equipment.
2. Description of the Prior Art
A hot isostatic pressurizing equipment (hereinafter referred to simply as HIP equipment) normally performs a processing in an atmosphere of inert gas such as argon or nitrogen. Recently, however, such HIP equipment sometimes employs argon gas mixed with oxygen as a processing gas.
In this instance, since a resistance to oxidation is required in a high temperature atmosphere, a platinum-rhodium alloy furnace or the like is used as a furnace mounted in a high pressure vessel. Meanwhile, such processing gas normally contains less than 20% of oxygen with respect to inert gas such as nitrogen.
On the other hand, a safety valve or a rupture disk is used as a safety device for a normal inert gas atmosphere HIP equipment.
In such a HIP equipment wherein gas mixed with oxygen is used as processing gas, control of a concentration of oxygen and control of a pressure are very important from the point of view of assurance of the safety. This is because, if oxygen of an excessively high concentration should be contained in processing gas in error, the HIP equipment may possibly be damaged, and if a pressure higher than a designed pressure is reached in error, the high pressure vessel or a pipe may possibly be damaged.
Control of an oxygen concentration, however, has not been executed so far. Instead, the internal temperature of a HIP equipment is controlled in order to prevent possible damage to the HIP equipment. Accordingly, there are the following problems.
In particular, in a HIP equipment, a furnace is covered with an insulation mantle so that the temperature within the high pressure vessel may not rise while a thermocouple is located on an inner face of a top closure of the high pressure vessel. Thus, if the insulation mantle is deteriorated and the temperature within the high pressure vessel rises to an extraordinarily high level, this is detected by the thermocouple to turn off power to the furnace.
However, if the concentration of oxygen in processing gas is high, then there is the possibility that a seal and a packing may be oxidized (burnt) by a rise of the internal temperature of the high pressure vessel. Accordingly, only turning off the power to the furnace in response to detection by the thermocouple may be too late for prevention of oxidation of a seal or a packing.
Further, in processing in an inert gas atmosphere, if a larger amount of oxygen than an allowable level is contained in processing gas, a graphite furnace or a molybdenum furnace will be worn by oxygen.
To the contrary, control of pressure within a HIP equipment has the following problems.
In particular, in a HIP equipment, a safety valve or a rupture disk is provided to relieve a pressure so that the pressure within the high pressure vessel may not exceed a predetermined designed pressure level.
However, if a higher pressure than the designed pressure level is reached when the concentration of oxygen in processing gas is high, then when a rupture disk is burst to relieve the pressure, a large amount of gas will be discharged at a time. Accordingly, there is the possibility that a pipe may be fired by some factor. It can be considered that the danger increases particularly where the temperature of the pipe is raised during such discharging of gas.